Genetics of ataxias: hereditary forms

Channelopathies Are a Frequent Cause of Genetic Ataxias Associated with Cerebellar Atrophy

Background

Cerebellar atrophy is a nonspecific imaging finding observed in a number of neurological disorders. Genetic ataxias associated with cerebellar atrophy are a heterogeneous group of conditions, rendering the approach to diagnosis challenging.

Objectives

To define the spectrum of genetic ataxias associated with cerebellar atrophy in a Canadian cohort and the diagnostic yield of exome sequencing for this group of conditions.

Methods

A total of 92 participants from 66 families with cerebellar atrophy were recruited for this multicenter prospective cohort study. Exome sequencing was performed for all participants between 2011 and 2017 as part of 1 of 2 national research programs, Finding of Rare Genetic Disease Genes or Enhanced Care for Rare Genetic Diseases in Canada.

Results

A genetic diagnosis was established in 53% of families (35/66). Pathogenic variants were found in 21 known genes, providing a diagnosis for 31/35 families (89%), and in 4 novel genes, accounting for 4/35 families (11%). Of the families, 31/66 (47%) remained without a genetic diagnosis. The most common diagnoses were channelopathies, which were established in 9/35 families (26%). Additional clinical findings provided useful clues to specific diagnoses.

Conclusions

We report on the high frequency of channelopathies as a cause of genetic ataxias associated with cerebellar atrophy and the utility of exome sequencing for this group of conditions.

The clinical application of transcranial direct current stimulation in patients with cerebellar ataxia: a systematic review

AIM

The aim of this review was to investigate the effects of transcranial direct current stimulation (tDCS) on motor function in patients with cerebellar ataxia.

MATERIALS AND METHODS

Our systematic review has been performed by searching full-text articles on Pubmed and Scopus. Only studies investigating the motor effects of tDCS in patients with cerebellar ataxias were considered. A qualitative analysis of data was performed, as the methodology of the selected studies was highly heterogeneous.

RESULTS

Our search yielded a total of twenty-seven hits. Based on the inclusion criteria, 19 of these were excluded and 89 were retained (number of patients = 81).The results reviewed so far suggest that tDCS over cerebellum combined or not with extra-cerebellar areas might be promising approach to improve motor outcomes, with a greater success in patients less impaired. In particular, it is been shown an improvement in both clinical measures assessing cerebellar deficits (i.e. gait, stance and oculomotor disorders) and performance measures (finger dexterity, upper limb coordination and gait speed). Some of the assessed investigations highlighted a restore effect of cerebellar brain inhibition pathway and resting motor threshold after tDCS.

CONCLUSIONS

tDCS could be considered an effective approach to promote plasticity in patient with cerebellar ataxia with significant motor effects. Future studies, with larger sample sizes are needed in order to evaluate the effective tDCS benefits on motor functionality. Due to the limited number of studies available so far, conclusions on the effectiveness of the reported approaches are premature.

Role of neuroimaging in the diagnosis of hereditary cerebellar ataxias in childhood

Hereditary ataxias are a heterogeneous group of neurodegenerative disorders, characterized by cerebellar ataxia as the main clinical feature, and a large spectrum of neurological-associated symptoms and possible multi-organ affection. Image-based approaches to hereditary ataxias in childhood have already been proposed. The aim of this review is to yield the main reports of neuroimaging patterns and diagnostic algorithms and compare them with the results from our study of 23 young patients addressed for ataxia, with subsequent genetic or metabolic diagnosis.